Regulatory mechanisms governing lytic growth and lysogeny in the life cycle of the temperate Salmonella bacteriophage P22 will be investiated. The initial work will be a continuation of genetic investigations including isolation of regulatory mutations, determination of their phenotype, complementation analysis, and genetic mapping. Plasmid derivatives containing restriction fragments of P22 DNA carrying regulatory loci will be constructed, and genetic methods for moving regulatory mutations into these plasmids from the P22 genome will be developed. Mutations in the Salmonella typhimurium chromosome which affect the decision between lysis and lysogeny after P22 infection will be isolated and characterized. Later stages in the investigation will include direct determination of nucleotide sequence of regulatory genes and sites of action and of mutations within them. Identification, assay, and protein purification will be undertaken for those regulatory proteins for which this has not yet been done (e.g., cl and mnt). Eventually studies of the mechanism of regulatory action of these proteins will be undertaken. A general method for transposing genes to episomes in vivo using flanking transposons will be developed, and methods for quickly mapping chromosomal mutations in Salmonella will be improved.